The use of mobile communications networks has increased over the last decade. Operators of the mobile communications networks have increased the number of base stations in order to meet an increased demand for service by users of the mobile communications networks. The operators of the mobile communications network wish to reduce the running costs of the base station. One option to do this is to implement a radio system as an antenna-embedded radio forming an active antenna array. Many of the components of the antenna-embedded radio may be implemented on one or more chips.
Nowadays active antenna arrays are used in the field of mobile communications systems in order to reduce power transmitted to a handset of a customer and thereby increase the efficiency of the base transceiver station, i.e. the radio station. The radio station typically comprises a plurality of antenna elements, i.e. an antenna array adapted for transceiving a payload signal. Typically the radio station comprises a plurality of transmit paths and receive paths. Each of the transmit paths and receive paths are terminated by one of the antenna elements.
The active antenna array or active antenna system is typically mounted on a mast or tower. The active antenna array is coupled to the base transceiver station (BTS) by means of a fibre optics cable and a power cable. The base transceiver station is coupled to a fixed line telecommunications network operated by one or more of the operators.
Equipment at the base of the mast as well as the active antenna array mounted on the mast is configured to transmit and receive radio signals within limits set by communication standards.
The code sharing and time division strategies rely on the radio station and the active antenna array to transmit and receive within limits set by communication standards. The communications standards typically provide a plurality of channels or frequency bands useable for an uplink communication from the handset to the radio station as well as for a downlink communication from the radio station to the subscriber device.
For example, the communication standard “Global System for Mobile Communications (GSM)” for mobile communications uses different frequencies in different regions. In North America, GSM operates on the primary mobile communication bands 850 MHz and 1900 MHz. In Europe, Middle East and Asia most of the providers use 900 MHz and 1800 MHz bands.
The operators have expressed a desire for an active antenna array that is able to utilise the existing base-station investments, in addition to providing services in a new frequency band. For example, in roll-out of long term evolution (LTE) at 700 MHz (US) or 800 MHz (EU), the operators would like to deploy a single antenna at the masthead which could transmit the existing 900 MHz (EU) or 850 MHz (US) GSM signals, using equipment at the base of the mast, as well as providing active antenna functionality for the new LTE installation.
One issue relating to adaptive antenna arrays is the inefficiency of the power amplifiers commonly used in the adaptive antenna arrays. The power amplifiers typically convert 20-40% of the power fed to them into radio signals. The rest, that is 60-80% of the power fed to the power amplifiers, is converted into heat and has to be dissipated. Failure to dissipate the heat will cause the power amplifiers to overheat, either resulting in an immediate failure or in a significant reduction of their lifespan.
The heat produced in the power amplifiers is dissipated by heat sinks. These heat sinks, together with their associated power amplifiers, are mounted on top of the mast, in the case of both active antennas and remote radio heads. In adaptive antenna arrays with a single frequency band, the heat sinks have a considerable size and weight. This weight adds a load on a mast of the radio station that the mast needs to be able to carry. Furthermore the heat sinks and associated power amplifiers, transceivers etc. also have to be transported to the top of the mast. This is not a trivial task and can require the use of cranes or ‘cherry pickers’, which are expensive to hire for the network operator. The operator does not, therefore, want to have to revisit the site regularly to remove faulty antenna systems from the masthead. One example of the heat sink used in an antenna is shown in US Patent Application Publication No US 2011/0032158 (Rodger et al, assigned to Andrew LLC).
The size and the weight of the heat sink capable of dissipating the heat generated by the power amplifiers required for two frequency bands, at the output levels desired by operators, is large. To date no such a heat sink is known to have been deployed at most existing base transceiver stations due to weight and size considerations.